RFR: CODETOOLS-7903261: Add FAQ entry about the time taken to run tests [v2]

[Jonathan Gibbons]

> Please review an update to the FAQ, to add an entry about the information recorded in `.jtr` files about test execution times.

Jonathan Gibbons has updated the pull request incrementally with one additional commit since the last revision:

  address review feedback; split recent entry into 2

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Changes:
  - all: https://git.openjdk.org/jtreg/pull/106/files
  - new: https://git.openjdk.org/jtreg/pull/106/files/faa1d918..9bff78a3

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jtreg&pr=106&range=01
 - incr: https://webrevs.openjdk.org/?repo=jtreg&pr=106&range=00-01

  Stats: 5 lines in 1 file changed: 4 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jtreg/pull/106.diff
  Fetch: git fetch https://git.openjdk.org/jtreg pull/106/head:pull/106

PR: https://git.openjdk.org/jtreg/pull/106